1. Technical Field
The present invention generally relates to determining line frequency. More particularly, the present invention relates to determining a line frequency presence and detecting a variable frequency artificial light source.
2. Background Art
In the past, various illuminant discrimination techniques have been used to determine the type of lighting present, for example, in a photographic scene. This information is useful to the photo developer for proper color correction, since different types of lighting cause different tinting of photos. Illuminant discrimination techniques exist not only to determine whether the light source is either natural or artificial, but also to determine among various types of artificial light, such as tungsten and fluorescent. If the lighting is artificial, the accuracy of these illuminant discrimination techniques may be adversely affected if the light samples are taken at a rate different from the line frequency of the artificial light source. Since line frequencies differ among countries, accuracy in the use of these artificial light discrimination techniques may be affected when traveling between countries.
Knowing the line frequency of an artificial light source would also be helpful in exposure setting techniques for cameras. If the line frequency is different from the light sampling rate for determining the correct exposure setting, light flickering can cause a light sample to be improperly interpreted, leading to an improper exposure setting. Thus, if the line frequency were known, light samples could be taken at the line frequency to avoid improper exposure due to flickering.
Thus, a need exists for determining a line frequency and a presence of a variable frequency artificial light source.